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31.
Rubies and sapphires are of both scientific and commercial interest. These gemstones are corundum colored by transition elements within the alumina crystal lattice: Cr3+ yields red in ruby and Fe2+, Fe3+, and Ti4+ ionic interactions color sapphires. A minor ion, V3+ induces slate to purple colors and color change in some sapphires, but its role in coloring rubies remains enigmatic. Trace element and oxygen isotope composition provide genetic signatures for natural corundum and assist geographic typing. Here, we show that V can dominate chromophore contents in Mogok ruby suites. This raises implications for their color quality, enhancement treatments, geographic origin, exploration and exploitation and their comparison with rubies elsewhere. Precise LA-ICP-MS analysis of ruby and sapphire from Mogok placer and in situ deposits reveal that V can exceed 5,000 ppm, giving V/Cr, V/Fe and V/Ti ratios up to 26, 78, and 97 respectively. Such values significantly exceed those found elsewhere suggesting a localized geological control on V-rich ruby distribution. Our results demonstrate that detailed geochemical studies of ruby suites reveal that V is a potential ruby tracer, encourage comparisons of V/Cr-variation between ruby suites and widen the scope for geographic typing and genesis of ruby. This will allow more precise comparison of Asian and other ruby fields and assist confirmation of Mogok sources for rubies in historical and contemporary gems and jewelry. 相似文献
32.
Lianxing Gu Khin Zaw Wenxuan Hu Kaijun Zhang Pei Ni Jinxiang He Yaotong Xu Jianjun Lu Chunming Lin 《Ore Geology Reviews》2007,31(1-4):107
More than 20 sediment-hosted massive sulphide deposits occur in Late Palaeozoic basins in South China. These deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their Cu, Pb, Zn, Au and Ag reserves. The deposits and their host strata were commonly intruded by Mesozoic granitoids. Remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein-, skarn- and porphyry-type orebodies in the same region or within a single deposit. The ore-containing basins occur in different tectonic settings. The Lower Yangtze basin occurs on a passive continental margin, where the deposits are high in Cu and Au with minor Pb and Zn and recoverable Ag, Co and Mo. The ores have a lower concentration of radiogenic lead, and δ34S values close to zero. Fluid inclusions are highly saline and Na-rich. Fluids and metals of the Lower Yangtze Region are interpreted to have been derived essentially from deep sources including the Precambrian basement. By contrast, basins of the Nanling Region formed in an intracontinental setting developed on a folded Caledonian basement. These deposits are higher in Pb, Zn, Sn and W, as well as Cu, with recoverable Ag, Sb, Hg, U, Bi, Tl and Mo. The ores are characterised by a higher concentration of radiogenic lead and a wide variation of δ34S composition. Fluid inclusions have lower salinities and higher K+/Na+ ratios. Fluids are considered to have been sourced substantially from seawater by convection. Metals for the Nanling deposits were essentially derived from the Caledonian basement by leaching. The contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore-forming basins. 相似文献
33.
Introduction
The Rheinisches Schiefergebirge, the northern,non metamorphic part of the Hercynian orogen in Middle Europe is one of the most excellent examples of a stable continental area, deeply weathered under a tropical to subtropical climate during upper Mesozoic and especially Paleogene periods. 相似文献